Senators weighing a landmark immigration bill defeated an effort by Republicans Tuesday to require biometric identification — such as fingerprinting — to track who is entering and leaving the country.

The amendment by Sen. Jeff Sessions, R-Ala., would have required a biometric system to be in place before any immigrant here illegally could obtain permanent residency or citizenship.

"This is a big, big hole in the system and it's gone on for years and years," Sessions said as the Senate Judiciary Committee opened its second day of meetings to plow through hundreds of amendments to legislation remaking the U.S. immigration system, a top priority for President Barack Obama.

"This is one of the reasons the American people have so little confidence in any of the promises we make," Sessions said.

An author of the bill, Republican Sen. Lindsey Graham of South Carolina, agreed with Sessions that biometric IDs are the most secure. But he said authors of the bill determined they were too costly to implement anytime soon. Indeed current law already requires such a system to be in place, but the Department of Homeland Security has been unable to implement it.

Instead the bill seeks electronic scanning of photo IDs.

"Current law is a concept, and there is apparently not a whole lot of will by Republicans or Democrats to make the concept a reality," Graham said. "What we've done is taken the current system and make it better."

Sen. Chuck Schumer, D-N.Y., said a biometric system would cost $25 billion. He and other Democrats said Sessions' amendment would simply throw up barriers to a path to citizenship for the 11 million immigrants already in the country illegally.

The Senate Judiciary Committee voted 12 to 6 to defeat Sessions' amendment. Graham and Sen. Jeff Flake, R-Ariz., joined with the Democrats on the committee in voting it down.

Graham, Flake, Schumer and Sen. Dick Durbin, D-Ill., are four of the eight authors of the immigration bill. Since they sit on the Judiciary Committee together they have resolved to vote together against amendments that could strike at the core provisions of the legislation and threaten the fragile alliances behind it.

Senators weighing a landmark immigration bill defeated an effort by Republicans Tuesday to require biometric identification such as fingerprinting to track who is entering and leaving the country.The amendment by Sen. Jeff Sessions, R-Ala., would have required a...